1. Field
One or more exemplary embodiments relate to a pressure sensor including a hybrid electronic sheet and a wearable device including the pressure sensor.
2. Description of the Related Art
Pressure sensors are widely used due to the commercial availability and popularity of mobile terminals or displays to which a touch-input manner is introduced. Touch-based pressure sensors are attracting attention for use in robots that measure and respond to external environments or stimuli, as well as use in electronic devices. Due to increasing recognition for the ubiquitous environment and technical development of humanoid robots, in addition to process robots that receive one-dimensional commands and repeatedly perform correspondingly, robots that respond and handle complicated and various environments or external stimuli by themselves are getting much attention. To voluntarily respond to external stimuli or environmental changes, such robots convert external stimuli or environmental changes into electrical signals through a tactile pressure sensing system mounted on their surfaces and voluntarily, flexibly respond to a command of a user.
Flexible device-based pressure sensors are available for use in, in addition to emotional electronic devices and humanoid robots, a sensor system that manages physical activities and regular sports activities. Flexible device-based super-sensitive pressure sensors can be used in a wearable sensor system that measures a heart pulse wave via the human skin or collects data about human walking and habits by attaching a pressure sensor to the sole of footwear. To embody such a wearable sensor system, there is a need to develop a sensor that includes a sensor basic unit having excellent bending and restoring properties, and excellent mechanical flexibility and stability.
Silicon-based solid MEMS-based pressure devices have a high level of accuracy, but due to their fragile property, they lack flexibility and are likely to crack, resulting in high difficulty for their application on various surfaces including a flexible surface. To develop a novel flexible electronic device having high mechanical flexibility, a conductive polymer, such as polypyrrole, PEDOT:PSS, or polyaniline, graphene, or a nano-structure material, such as carbon nanotube (CNT), metal nanoparticle, or metal nanowire are getting attention as an alternative to silicon. In particular, CNT is an alternative to ITO, which is conventionally used, due to its high light transmissibility and conductivity. CNT also has excellent chemical stability and mechanical characteristics. Furthermore, the recent advance in synthesis technology enables mass-production of CNT, decreasing manufacturing costs thereof. However, in the case of conductive polymer-based pressure sensors, their long-term stability and, when in contact with moisture, their conductivity may change significantly. Accordingly, this material is inappropriate for a pressure sensor. In the case of nano material-based devices, in view of properties of nano materials, it is difficult to obtain reproducibility.
Accordingly, there is a need to develop a pressure sensor that has excellent controllable electrical properties so that it is usable/applicable in various fields including humanoid-based robots, smart vehicles, aerial applications, simulation, process control, human being-friendly IT, fingerprint-recognition systems, bio-monitoring smart sensors, or the like, and that has excellent mechanical flexibility and stability.